<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- <ul>
        <li>
            北京市
            <ul>
                <li>海淀区</li>
                <li>昌平区</li>
                <li>朝阳区</li>
            </ul>
        </li>
        <li>
            河北省
            <ul>
                <li>石家庄</li>
                <li>保定</li>
            </ul>
        </li>
    </ul> -->

    <!-- <script>
        var num = 10;
        if (true) {
            var num = 20;
            console.log(num);
        }
        console.log(num);
    </script> -->
    <script>
        let num = 10;
        if (true) {
            let num = 20;
            console.log(num);
        }
        console.log(num);
    </script>
</body>
</html>